Particulates suspended in the atmosphere originate from a wide variety of biogenic and anthropogenic sources. Water-soluble species include inorganic cations (ammonium, potassium, calcium, sodium, and magnesium), inorganic anions (sulfate, nitrate, nitrite, chloride), some heavy metals, and water-soluble organic carbon species such as oxalate, other organic acids, carbohydrates, and organic amines.
Most often these constituents are measured by in-field collection on a filter, followed by offline, laboratory-based sample extraction and analysis. Generally the time resolution is poor, and results are not known for several weeks after the collection. Inorganic ions in atmospheric particles can also be measured in-situ by coupling a steam injection particle collector to an ion chromatography analyzer.
Microchip capillary electrophoresis is an inherently less expensive and less bulky method than ion chromatography. It is more sensitive, with much lower detection limits on a mass basis. It is much faster, with separation times of the order of one minute as compared to several minutes or longer for ion chromatography. “Lab on a chip” is an established approach for the chemical analysis of solutions wherein many of the components required for the analysis are incorporated onto a microchip. Generally speaking, these microchips contain a sample reservoir that holds the solution to be analyzed, a separation channel for separating the analytes of interest from other constituents, and a means of detecting those constituents after separation. Through the application of electrical voltages or hydrodynamic forces, a small amount of solution is moved from the sample reservoir to the beginning of the separation channel. The analytes travel down the separation channel with a characteristic migration time dependent on the analyte, and are detected when they arrive at the end of the channel. The separation can be done by electrophoresis, where ions move under the influence of an electric potential difference applied across the channel. Detection can be done by measuring the change of electrical conductivity of the solution.
The prior technology requires that the solution to be analyzed be placed in the sample reservoir by pipetting or otherwise physically placing the solution into the sample reservoir.